Typically, close positioning or modulating control of electric motors requires the use of special start/stop or jogging equipment. In addition, because of the higher duty cycle, a non-standard motor having a higher temperature rating is usually required. Each attempt to start the motor generates heat within the motor, and repeated attempts will result in overheating and destruction of the motor if a standard motor is used. The use of such a non-standard motor having a higher insulation temperature rating significantly increases the overall cost of the system.
Most close positioning or modulating control systems also utilize a gear reducer on the output of the electric motor. Due to the inertia of the motor and gear reducer, the desired new position of the motor is "overshot", and the motor needs to be reversed in order to assume the proper position. Motor reversal may also be due to the need to establish a new position. This reversal requires a disproportionate motor movement due to gearing "backlash". Repeated energization or jogging to provide the fine tuning of the position also contributes to the overheating and destruction of the motor. Thus, the use of a non-standard motor in presently available close positioning or modulating control systems is imperative.
Because of the foregoing, it has become desirable to develop a controller for close positioning or modulating control of a motor which can be utilized with a motor having a standard insulation temperature rating without the possibility of overheating the motor during repeated close positioning of same.